1. Field of the Invention
The present invention relates to semiconductor device packages and lead frames therefor and, more specifically, the invention relates to a high power semiconductor device adapted for surface mounting.
2. Related Art
Packages for high power semiconductor devices which can be surface mounted on flat support board surfaces are well known. One such package is shown in U.S. patent application Ser. No. 08/583,219, filed on Jan. 4, 1996, entitled SURFACE-MOUNT SEMICONDUCTOR PACKAGE which is incorporated herein by reference. Such packages are very well adapted for surface mounting to the conductive patterns of a flat support board, such as an IMS structure (a thick copper or aluminum substrate covered by a thin insulation film which has a thin patternable copper or other conductive solderable upper surface).
It is known to provide a pattern of shallow spaced indentations (or waffles) on one surface of the metal heat sink pad of the prior art surface mount packages, which surface couples to the semiconductor die. It is known that the waffle pattern improves the solder down of the die to the waffled surface.
Of critical concern to designers in the art is the solder down characteristics of the metal heat sink pad of the package to the IMS board. In high power applications, the solder down of the metal heat sink pad is of particular importance because of the need for good heat dissipation.
Surface mount packages of the prior art are designed with metal heat sink pads having smooth flat surfaces, which smooth flat surfaces are soldered to substrates (such as IMSs). Unfortunately, the smooth flat surface of the metal heat sink pad often does not properly wet with solder which results in poor contact with the IMS. Further, when the surface is slightly concave, undesirable solder voids result.
Consequently, heat transfer from the surface mount package to the IMS is adversely affected and elevated die temperatures result (possibly damaging the device). Further, the mechanical integrity of the package to IMS junction may be degraded resulting in poor ruggedness and susceptibility to failure, particularly under vibration. The above disadvantages are exacerbated when the package size increases, and the surface area of the metal heat sink pad correspondingly increases, which is the typically the case in high power devices.
Accordingly, there is a need in the semiconductor packaging art for an improved surface mount package with superior solder down characteristics to the substrate resulting in better thermal and mechanical performance.